crossettes

I made some crossettes last summer,on new years eve i made a cake and
put some of them in the tubes.they all worked great,but they popped way
to early,and the 4 pieces fell to the ground.
These were hand pressed with a homemade press and a bottle jack.
my question is, does pressure have anything to do with burn speed.
if i added more comp and pressed them with an arbor press yet they were
still the same size would they burn slower.BTW this comp was homemade
b.p. with aluminum and extra charcoal added,it made a great effect,and
received the most praise out of everything i did.i just need them to go
higher for safety.
thanks
Joe